1. I've seen a post that states that
if you do something, your party becomes "evil". Search the forum. I've never been evil so that I don't know.
At any rate, your evilness has no consequences. Most likely, the good-neutral-evil orientation was planned but not implemented in the game.
2. Erathsmedor cannot be killed, harmed, or even Vanished while it is flying in the exterior. Anephas can be killed in the Cet's room when you side with Cet - but only with a black flame boosted Mavin Sword of Staff of Death. Note: Anephas is more than 800 000 XP, he is worth of much more XP than Cet
I've seen a post (it's somewhere on this forum) with instructions how to kill G'Ezzered Ra. You must get him out of his room because he is immune to anything there. I've never tried it.
Other "monsters" that cannot be killed or even harmed: Ghost of Nivius, all Oracles. Kerah and Kol are cheating: Kerah can lose HP but only to a certain level, then she becomes immune to anything even if you will be getting messages "Kerah was hit for nnn HP". Kol is cheating from the beginning. He is immune to anything even if you will be getting messages "Kol was hit for nnn HP".
3. Hmmm, Kerah? Evil? Why?
4. Bsftcs' solution seems to be the only solution of giving the Holy Water to the flying Kerah.
5. Book of Misfortune does nothing. Perhaps, there was a spell named Misfortune planned during the game development but it wasn't implemented.
Misfortune is a "level 1 spell" so that the book isn't worthy to pick.
6. Bard isn't my favorite class. I haven't detected any special feature of a bard worth of mentioning.
But bard seems to be the only class that can gain Trickery trait. The trait is useful. Therefore:
1. Pretend to change role to a Bard.
2. Get the Scroll of Trickery. Give it to a mule in the inn and cancel Bard training.
3. Wait until you reach level 5 in Pawn Shop and until you get training rights there.
4. When you decide to change role to anything, become a Bard first (by means of the previously gained scroll), get the Trickery trait and then change role again to the decided role without leveling up as a Bard. This will block the Music skill so that it won't appear on your skill list.
7. It's a flaw in the game logic. Use Guild Hopping and join the Warriors Guild or Bushi Dojo. They teach 2nd Weapon skill.